User Guide: Technical Reference
SECTION 2
ioLink 4
SYSTEM COMPONENTS
PRELIMINARY
Customer Support (202) 333-7031
2-12
As mentioned in the Advanced Menu section, the
ioLink 4
has a menu item that displays the Pre-FEC
BER. This gives the user an indication of how many errors the unit receives prior to the signal going to the
FEC circuitry in the modem unit.
This menu item does not display the BER once the signal is corrected for errors, since the post-FEC BER
cannot be determined very accurately by the very nature of how FEC works. The BER that the user
equipment sees is much better than that displayed on the Pre-FEC BER menu item.
Although the post-FEC BER cannot be exactly determined, it can be estimated. The following chart
shows approximately how the BER is improved by the particular FEC scheme that is used in the modem
unit. This chart assumes that the errors are introduced into the signal periodically rather than in bursts.
For example, this chart may represent BER improvement given a uniform average of 300 errors per
minute (i.e., 5 errors every second). The chart would look different for bursts of 300 errors every minute
(i.e., all 300 errors occur at the end of each minute).
